JB makes a good tool, find it in almost any wholesale house. If the copper is older, need to take your torch and heat up the copper until it turns dark and let it cool on it's own. then crimp the line, pump down the system, make your repair, put the crimped end in the circular part and walla! you just saved yourself 2 hours not recovering the system. I've done it dozens of times..... works great every time!
OH, another little secret. take those tiny little nuts off that comes with the tool and sling them far as you can and go get two nuts they use to splice all thread with, you will not strip them out like you would the nuts that come with the tool. Happy crimping!